Biological Features and Ecology
The causative agent of tinea versicolor belongs to the group of yeast-like fungi. In older taxonomic classifications, this microorganism was known as Pityrosporum orbiculare. Today, the genus Malassezia includes considerable species diversity: in addition to M. furfur itself, eleven other species are identified, among which M. globosa also holds significant clinical importance.
A key physiological feature of the pathogen is its lipophilicity. This means that complex fatty acids are vital for the fungus's normal metabolism and reproduction. This physiological requirement determines its natural localization: M. furfur is a legitimate member of the normal human skin microbiota and predominantly colonizes areas with the highest sebaceous gland activity.
Pathogenesis and Clinical Presentation
Upon transitioning from a commensal to a pathogenic state, M. furfur causes a specific condition known as tinea versicolor (also called pityriasis versicolor).
The pathological process has a strictly limited localization: the fungus infects exclusively the most superficial parts of the stratum corneum. Anatomically, the lesions are most commonly located on the skin of the trunk, neck, and upper extremities.
Characteristic features of the rash:
- Visually, they appear as pinkish-yellow macules.
- The spots are strictly non-inflammatory.
- The so-called "variegation" is observed: hyperpigmented (darker) and hypopigmented (lighter) lesion areas are simultaneously present on the patient's skin.
- A critical diagnostic sign: gentle scraping of the spot's surface reveals characteristic scaling, with the detachment of fine scales that strongly resemble bran (hence the name pityriasis, from Greek furfur meaning bran).
Microscopic Diagnostics
Laboratory diagnosis of tinea versicolor begins with direct microscopy of pathological material. Skin scales taken from the lesions serve as the test sample.
To better visualize the fungal elements, the scales are pre-treated with a 20% alkali solution, which dissolves keratin and clears the specimen.
What can be seen under a microscope (in pathological material):
- Yeast-like budding cells that frequently cluster in grape-like bunches.
- Pseudomycelium, represented by short and slightly curved hyphae (filaments).
This combined presence of elements in the scales is a classic microscopic pattern for this disease.
Culture Methods
Isolation of a pure culture of M. furfur requires special conditions due to the pathogen's specific nutritional requirements. Sabouraud agar serves as the basal medium, supplemented with an antibiotic (tetracycline) to suppress accompanying bacterial flora.
Cultivation specifics:
- Mandatory requirement: presence of lipid components. To ensure lipophilicity, Tween-80 is added to the nutrient medium or sterile olive oil is applied to the surface.
- The incubation period for colony growth is about one week.
- Grown colonies are white and have a characteristic cream-like consistency.
Microscopy of the culture itself (unlike material from scales) reveals only oval or bottle-shaped budding cells measuring $2 \times 6$ \mu{}m. Important note: true mycelium is completely absent in this fungus.
Treatment Approaches
Since the causative agent is a fungus, therapy is based on antimycotic (antifungal) drugs. According to clinical data, the following medications are used to suppress M. furfur activity:
- Amphotericin B;
- Itraconazole;
- Ketoconazole;
- Fluconazole.